For the first half of the novel, I was into it. The writing is not the strongest I've read but aimed at younger children, so it wasn't too distracting. I wanted to see how all the elements would tie into the Oz mythology.
Then some point around the half-way mark of the book the plot seemed less structured. Elements like Donny's mother's despair and the constant running and hiding began to bother me. The end of the book was a disappointment, as it became clear that certain parts of the story would not be explained (the identity of the strange woman who sold them the shoe) and other things would be drawn out for a possible sequel (the sorcerer being stranded in our world).
So: for its own sake, I thought the novel was on the weaker side. As an added bit of Oz world, there are some creative and interesting ideas here--I liked the bits about L. Frank Baum. On the other hand, I didn't like the idea that the silver shoes themselves were malevolent. Some good and some bad here. Worth reading if you're very into Oz and looking for something new, but otherwise you might pass this one.